| Abstrakt: |
This paper describes the synthesis of a series of titanium and zirconium metallocenes bearing one or two first-generation silane dendritic wedges as bulky substituents at their cyclopentadienyl rings. Wedges (R2R'SiCH2CH2)3SiCl [R = R' = Et (1); R = Ph, R' = Me (2)] were prepared by hydrosilylation of chlorotrivinylsilane with R2R'SiH. They were reacted with K(C5H5) and, subsequently, with KH to give K[(R2R'SiCH2CH2)3Si(C5H4)] [R = R' = Et (3); R = Ph, R' = Me (4)]. The dendronized cyclopentadienides 3 and 4 were the starting materials for preparation of the mixed-ring titanocenes [{(R2R'SiCH2CH2)3SiC5H4}(C5R''5)TiCl2] [R = R' = Et, R'' = H (5), R'' = Me (6); R = Ph, R' = Me, R'' = H (7), R'' = Me (8)] or the symmetrically substituted metallocenes [{(Ph2MeSiCH2CH2)3SiC5H4}2MCl2] [M = Ti (9), Zr (10)]. Cyclic voltammograms and catalytic behavior of all the new metallocenes in ethylene polymerization, using MAO as a cocatalyst, have been studied and compared to that of related non-dendritic complexes. Polyethylene polydispersities increase with the number of dendritic wedges in the catalyst, while activities decrease. Bimodal molecular weight distributions were clearly observed for the bis-dendritic titanocene 9. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002) |
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